The SAAgent class extends the Android service and handles asynchronous Accessory-related intents. Its implementation executes all of its activities in a worker thread, which means that it does not overload your application main thread.

3. Defining the Accessory Service Profile

Communicating with a remote Peer Agent requires the declaration of descriptions about the Accessory Service Profile. This is declared in a separate file in the /res/xml folder in your application project. The path of the actual XML file can be added in the application’s AndroidManifest.xml file.

When the application is installed, the Samsung Accessory Service Framework automatically registers its Accessory Peer Agents using the information specified in your service profile XML file. Similarly, the Accessory Peer Agents are deregistered when the application is uninstalled. An error log is dumped if the registration process fails to register the Accessory Service Profile implementation. To define the Accessory Service Profile, see Validating Accessory Service Profile XML in this.

4. Setting up the Service Connection

If the application wants to establish a service connection with only one Accessory Peer Agent, check the first callback. You can also check the identity or properties of the discovered Accessory Peer Agents by calling the functions provided by the SAPeerAgent class to decide which Accessory Peer Agent you want to form a service connection with. The application can initiate a service connection with an Accessory Peer Agent by calling the SAAgent.requestServiceConnection() function.

This function is called from a worker thread. If you need to do any heavy lifting or long latency work in the callback, spawn a separate thread.

If a service provider connects only with a specific service consumer, or a service consumer with a specific service provider, the service provider and consumer are called ”companion applications”. When you only want to connect to a companion service provider or service consumer, call the functions provided by the SAPeerAgent class for specific information, such as model number or vendor information, before calling the SAAgent.requestServiceConnection() function. For example, when a photo printer service provider on an accessory device from a company only wants to connect to a photo printer service consumer on a smart device from the same company, they are companion applications.

The remote Accessory Peer Agent either accepts or rejects your service connection request. Your application is notified with the SAAgent.onServiceConnectionResponse() callback. The request can be accepted (and a service connection established) or rejected, or it can fail to establish the service connection for other reasons.

When a service connection is successfully established, the requesting Accessory Peer Agent gets an instance of the SASocket object, which is used to handle service connection events and send or receive data to and from Accessory Peer Agents.

5. Handling the Setup Service Connection Request

SAAgent.onServiceConnectionRequested() callback when a remote Accessory Peer Agent wants to create a service connection with it:

The Accessory Peer Agent implementation can accept or reject service connection requests by calling the acceptServiceConnectionRequest() or rejectServiceConnectionRequest() function.

The default implementation of the SAAgent.onServiceConnectionRequested() callback is to accept every incoming service connection request from any remote Accessory Peer Agent. Your Accessory Peer Agent implementation can override this function, usually to check the identity and properties of the requesting remote Accessory Peer Agent before accepting or rejecting incoming service connection requests.

The SAAgent.onServiceConnectionRequested() callback can check for Accessory Peer Agent-specific information before accepting service connection requests. You can use the SAPeerAgent object functions for checking specific information, such as application name or vendor ID.

If your application accepts the service connection request, your application is notified through the SAAgent.onServiceConnectionResponse() callback when the service connection is established or a failure occurs. On success, an SASocket object is passed with the callback. If you want to implement a service provider application that can serve multiple service consumer applications at the same time, keep a repository of the SASocket objects for all active service connections, and give an identifier for each SASocket object.

The SAAgent.onServiceConnectionResponse() callback is called from a worker thread. If you need to do any heavy lifting or long latency work in the callback, spawn a separate thread.

6. Exchanging Data with the Accessory Peer Agent

Call the SASocket.send() function of the SASocket object (passed with the SAAgent.onServiceConnectionResponse() callback) to send data on the selected service channel inside an established service connection. The Samsung Accessory Service Framework provides a datagram service. Either all the data is sent or nothing is sent. The service connection encapsulates all service channels as defined by the Accessory Service Profile specification.